Search for survivors and bodies continues in New York
On Thursday Mayor of New York Rudolph Giuliani said the list of people missing had risen to nearly 5,000.
It is believed many more may have been killed when two passenger jets crashed into the World Trade Center, causing the twin towers to collapse on Tuesday.
The spirits of rescuers were raised as five firefighters were pulled from the rubble in New York, two days after the attacks, but there are concerns what the site remains unstable because of damage to surrounding buildings.
The British Government has said the number of Britons confirmed dead is about 100 and it is feared more than 500 were killed.
The Irish Department of Foreign Affairs has confirmed four Irish people were killed in the attacks.
The department said it expected the eventual Irish toll to be in double figures, as fears grow for a number of Irish citizens who were working in the vicinity and are still missing.
Dublin man, Patrick Currivan, 53, was on one of the hijacked planes which crashed into the World Trade Center.
He was a senior executive with the French stock exchange.
She had been living in Connecticut. Her brother Ronnie, who was working in the twin towers, managed to escape.
Speaking on Thursday he said: "The people who killed her just don't belong in civilised society."
Others feared dead
A cousin of the County Tyrone Gaelic football players Peter and Pascal Canavan is feared dead.
Sean Canavan, a 38-year-old carpenter, was finishing off a job on the 94th floor of the south tower when the attacks happened.
His cousin Niall Kilpatrick said the family feared the worst.
Meanwhile, the family of a man from County Sligo who was working in the world trade centre have said that he has been missing since Tuesday.
Kieran Gorman, 35, of Carrowcurragh in Lavagh, was working as a labourer on an upper floor of one of the towers when the attacks happened.
Shortly after the attack on the first building, he phoned his wife Ann on his mobile phone and said: "We're getting out".
'I'm trying to get out'
Irish carpenter Martin Coughlan, 53, from County Tipperary, is also missing.
He last spoke to his wife Catherine on the phone from the lift on the 96th floor of the south tower just after the second hijacked plane plunged into the skyscraper complex.
Martin and Catherine Coughlan lived in the Queen's district of New York after moving with their four daughters to the US 14 years ago.
Martin's sister-in-law, Josie Coughlan said the family is devastated.
She said: "Catherine is devastated. They tried the hospitals yesterday looking for Martin but it looks bleak."
Last seen
Anne Marie McHugh, 35, from Galway, worked in an office on the 84th floor of Tower 2.
Her family believe she was last seen on Tuesday morning on the 40th floor as she tried to leave the building.
The family of Bill Deane, 35, from Donegal has also said he is feared missing.
He had been working on the 100th floor World Trade Center for an insurance company, when the tower was struck by the first plane.
Damien Meehan, also from Donegal family, who was working on the 92nd floor, is also missing since the attacks.
A Foreign Office emergency number for British people worried about friends and relatives has also been issued: 020 7008 0000.
The Dublin Department of Foreign Affairs has also released an emergency number: 00 353 1 408 2000.